One of the things you come across when you understand how to geocache, are geocoins.
Gecoins are trackables that are used in geocaching. They are large custom made coins, usually moulded rather than pressed, with a coloured artwork applied and baked.
Geocoins are often beautiful works of art and many that get (*cough* stolen) lost. I can't understand the mindset of someone who will deliberately take one of these coins and then not log it. Some of them are worth a bit of money.
Here are some places where you can obtain geocoins: